1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEMATIC SERVICES TERMINAL EQUIPMENTS AND PROTOCOLS FOR TELEMATIC SERVICES T.564 (03/93) GATEWAY CHARACTERISTICS FOR VIDEOTEX INTERWORKING ITU-T Recommendation T.564 (Previously “CCITT Recommendation“) - STD
2、-ITU-T RECMN TeSbLi-ENGL 1793 = qBb257L 0b2027Li T7Li FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecorn- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on
3、 them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Rec
4、ommendation T.564 was revised by the ITU-T Study Group VI11 (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the
5、ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to referenc
6、es containing the acronyms “CCITT, CCR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency.
7、In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 AI1 rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission
8、 in writing from the ITU. I 2 3 4 5 6 7 8 9 10 CONTENTS Introduction Scope and field of application 2.1 National videotex services 2.2 Videotex interworking definition 2.3 Relation to other Recommendations . References Definitions Abbreviations . Model of the communication between local and external
9、 host 6.1 International videotex interworking between gateways 6.2 Position of videotex interworking relative to OS1 6.3 Organization of the videotex interworking . Relation between videotex and DTAM service . Use of lower layer services General structure of the VIA 9 .I General data structure . 9.2
10、 Attributes . 9.3 General VIA operation . Videotex structure 10.1 Display structure . 10.2 Data entry structure . 10.3 Administrative structure . 10.4 Special terminal facilities structure . Annex A . Layout structure and operational structure Annex B . Minimum size of data structures . Recommendati
11、on T.564 (03/93) Page 1 1 1 1 1 1 2 3 3 3 4 4 5 6 6 6 7 8 8 9 IO 26 28 30 30 I Recommendation T.564 GATEWAY CHARACTERISTICS FOR VIDEOTEX INTERWORKING (Melbourne, 1988; amended at Helsinki, 1993) 1 Introduction This Recommendation specifies gateway characteristics which should be used for internation
12、al videotex interworking between gateways. This Recommendation is a part of a set of standards produced to facilitate the interconnection of national videotex services. This set of standards is positioned with respect to the open systems interconnection basic reference model (see Recommendation X.20
13、0). This Recommendation lies within the field of application layer of the OS1 application layer. Inside the application layer it makes use of DTAM (document transfer, access and manipulation) specific application service element (see Recommendation T.400). 2 This Recommendation applies to the intern
14、ational videotex interworking between gateways as specified in this clause. Scope and field of application 2.1 National videotex services It is the responsibility of Administrations to decide the configuration of the national videotex services. 2.2 Videotex interworking definition Videotex interwork
15、ing allows a videotex terminal pertaining to a given videotex service of a given country to interact in real time with a videotex host computer located in a different couny. This videotex host may be either a videotex center or an external computer. 2.3 Relation to other Recommendations Videotex int
16、erworking gateway characteristics are based upon concepts of DTAM defined in the T.400-Series Recommendations. Videotex interworking conforms to the videotex service defined in Recommendation F.300 and it is specified by the following profiles: - - - a document application profile specified in Recom
17、mendation T.504; a communication application profile specified in Recommendation T.523; an operational application profile specified in Recommendation T.54 1. General concepts of the international videotex interworking and the data syntaxes relevant for the videotex interworking are defined in Recom
18、mendation T.lO1. 3 References - Recommendation F.30 Videotex service. - Recommendation X.200 (1988) Reference model of open systems interconnection for CCITT applications. Recommendation X.213 (1992) Information technology - Network service definition for open systems interconnection. Recommendation
19、 X.214 (1988) Transport service definition for open systems interconnection for CCITT applications. - - Recommendation T.564 (03193) 1 - Recommendation X.224 ( 1988) Transport protocol specification for open systems interconnection for CCITT applications. Recommendation X.215 (1988) Session service
20、definition for open systems interconnection for CCITT applications. Recommendation X.225 ( 1988) Session protocol specification for open systems interconnection for CCIlT applications. Recommendation X.216 (1988) Presentation service definition for open systems interconnection for CCITT applications
21、. Recommendation X.226 ( 1988) Presentation protocol specification for open systems interconnection for CCIT appficarions. Recommendation X.2 17 (1992) Service definition for the Association Control Service Element. Recommendation X.227 ( 1992) Connection-oriented protocol specification for the Asso
22、ciation Control Service Element. Recommendation T. 1 O1 International interworking for videotex services. Recommendation T.400 (1 988) Introduction to document architecture, transfer and manipulation, - - - - - - - - - Recommendation T.411 (1988) Open document architecture (ODA) and interchange form
23、at - Introduction and general principles. Recommendation T.412 (1988) Open document architecture (ODA) and interchange format - Document structures. Recommendation T.4 14 ( 1988) Open document architecture (ODA) and interchange format - Document profile. Recommendation T.415 (1988) Open document arc
24、hitecture (ODA) and interchange format - Open document interchange format (ODIF). Recommendation T.43 I (1988) Document transfer and manipulation (DTAM) - Services and protocols - Introduction and general principles. Recommendation T.432 ( 1988) Document transfer and munipulation (DTAM) - Services a
25、nd protocols - Service definition. Recommendation T.433 (1988) Document transfer and manipulation (DTAM) - Services and protocols - Protocol specification. Recommendation T.44 1 ( 1988) Document transfer and manipulation (DTAM) - Operational structure. Recommendation T.504 Document application profi
26、le for videotex interworking. Recommendation T.523 Communication application profile DM- I for videotex interworking. Recommendation T.54 1 Operational application profile for videotex interworking. - - - - - - - - - - Definitions The following definitions apply to all other parts of the Recommendat
27、ion. This Recommendation makes use of the following terms as they are defined in Recommendation F.300: - videotex access point; - videotex frame; - videotex gateway; - videotex host; - videotex service; - videotex service center; - videotex terminai; - videotex user. 2 Recommendation T.564 (03/93) S
28、TD-ITU-T RECMN T-SbLi-ENGL 1773 LiAb2.571 0b202.78 b1T = This Recommendation makes use of the following terms as they are defined in Recommendation T.400: - attribute: - content portion: - page; - block; - specific layout structure; - subordinate. 5 Abbreviations For the purpose of this Recommendati
29、on, the following abbreviations are used: ACSE Association control service element CASE Common application service elements DDA Defined display area DTAM Document transfer, access and manipulation OS1 Open systems interconnection SASE Specific application service element SE Structure element VIA Vid
30、eotex interworking architecture 6 Model of the communication between local and external host 6.1 Videotex interworking may take place between videotex services in different countries, independently from the national configuration being used. An abstract configuration model has been established in Re
31、commendation F.300 to represent an international videotex interworking configuration using gateways. In this abstract model, each cooperating country is represented by a videotex gateway. The DTAM protocol is intended to be used between the two gateways. Consequently a typical communication may be d
32、escribed as shown in Figure 1. International videotex interworking between gateways Country A Country B Videotexhost National d supporting the local application process. The Videotex Interworking Architecture (VIA), the DTAM service and the DTAM protocol correspond to the communicating part of the a
33、pplication process and represent those aspects of the application process which are pertinent to OSI. The VIA is a virtual data structure with a set of possible actions that can be performed on it. This structure is used to represent the current state of the communication between the two application
34、s processes. 4 Recommendation T.564 (03/!33) STDmITU-T RECMN T-5bLi-ENGL 1793 Lidb2571 Ob20280 278 Any operation on VIA must be reported to the peer entity and to the Videotex service user. These operations are reported to the peer entity by using the DTAM service which is provided by the DTAM proto
35、col. a) In the first dialogue step, the external host defines a data entry program which describes all the actions the local host must follow when the user enters data. This data entry program contains the description of the form, i.e. the description of the different areas of the screen where entry
36、 will be performed. It also contains the reactions to users inputs the local host has to follow. These reactions, called rules, contain e.g. the list of allowed character, the type of echo to be performed, the list of possible commands, etc. Moreover, a guidance message, called prompts, may be assoc
37、iated with each Field. Theses messages are displayed each time the cursor reaches or leaves the corresponding Field in order to give to the user some information about the filling of the form; When the local host then receives the run (in the case of duplex mode) the local host immediately sends it
38、back to the external host. It then executes the defined data entry program till encountering an event which provokes the termination of the entry. This events must be one of the termination reasons defined by the external host and correspond either to a valid user command or to the running out of a
39、time-out or to the entire filling of a field. The termination reason is reported back to the external host as the second dialogue step. According to the regulations of the Videotex service at the local host side, the report may or may not contain the data entered by the Videotex user. NOTE - Figure
40、3 is for information on the videotex interworking organization only. b) Videotex seMce 1 Vdeotex service 2 lZSS application I DTAM protocol 4 application I L I To81 862c-94/603 FIGURE 3.564 7 Relation between videotex and DTAM service (see Figure 4) This clause does not form an integral part of this
41、 Recommendation. The local application process is in charge of the local mapping between the communicating OS1 environment and the videotex service as defined by a given Administration. On the local host side, the local application process is in charge of converting the local host to external host d
42、ialogue into a videotex user dialogue. On the external host side, the loca1 application process is in charge of converting the external host to local host dialogue into a national videotex host access dialogue. The two local application processes are able to communicate on an international basis by
43、updating both their own and the peer entity VIA, which represents the common view of the communication as seen by both partners. To indicate that a VIA update is needed, the local process may express all the VIA modifications as DTAM service elements through the DTAM service interface. Any modificat
44、ion of the VIA must be reported to both the local and the remote users. When receiving a DTAM service primitive, the VIA is updated and the receiving local application process takes the updating into account. Recommendation T.564 (03/93) 5 STD*ITU-T RECMN T.Sb4-ENGL 1793 48b2571 0620281 104 Videotex
45、 service DTAM service I I I I I I I I I I I 8 I , bdF /, I I application process ! I I T18630-94/d4 FIGURE W.54 For a given definition of a videotex service, several local application processes may exist with different levels of complexity. For example, a given local application process may not take
46、 into account the existing VIA, or for each new frame to be displayed, delete the existing VIA and create a brand new one. A more clever local application process may, on its own, take care of the previous VIA and express through the DTAM service interface the sole modification of the VIA. It is up
47、to the Administrations concerned to define all the details of the local application process to communicate through the DTAM service, which supports the local application process. 8 The use of lower layer services is specified in Recommendation T. 10 I. Use of lower layer services 9 General structure
48、 of the VIA 9.1 General data structure The following list is a basic set of requirements for the properties of a general data structure handled by the videotex interworking gateway. Videotex interworking is an application profile on top of DTAM and the videotex interworking architecture (VIA) is in
49、line with the general structuring principles defined in Recommendation T.400. The VIA consists of a document profile, an operational profile and five data structures: - - a specific layout structure: the display structure; four operational structures which are used to carry: i) the data entry structure; 2) 3) the administrative structure; 4) the application control memory structure; the special terminai facilities structure. NOTE -Only one operation profile is used for the four concerned operational structures. The data structure is composed of structure elements (SE) which can be man
